Intense drought in southern tier in no hurry to loosen grip

Prospects are bleak for relief in Louisiana, Oklahoma and Texas

There continues to be a dramatic schism dividing Americans. No, I’m not talking about contrasting ideas on what to do about the federal deficit, chronic unemployment, or which candidate to favor in the upcoming 2012 elections, divisive as these matters may be in Washington these days. Instead, I’m referring to the stark contrast between the precipitation “haves” and “have-nots” in this country, which is another divide that is getting wider with time.

Several weeks ago, I called attention to the fact that, throughout this spring and early summer, many Americans have concurrently witnessed some of the worst flooding in recent memory and one of the worst droughts in their lifetimes. The stark juxtaposition of floods and drought is remarkable, and it’s showing no signs of abating. In fact, according to federal forecasters, flood risks are likely to remain high during the rest of the summer in parts of the Upper Midwest and West, while the drought hangs tough – or even intensifies its grip on a portion of the South.

In this post, I’m going to focus on the drought, which is a far less visible, but no less damaging force of nature compared to the Mississippi and Missouri River floods.

At a drought conference in Austin, Texas last week, climate forecasters delivered unwelcome news to water resource managers and other policy makers – the chance for significant drought relief during the next three to six months is extremely low in Texas, and many other portions of the expansive drought area that stretches from Arizona to Virginia.

Even if a tropical storm or hurricane were to make landfall in Texas during this hurricane season, it would be unlikely to dramatically lessen the drought’s severity in the Lone Star State, said Dan Collins, a forecaster for NOAA’s Climate Prediction Center, who took part in a media conference call from the drought meeting.

Marty Hoerling, a researcher with NOAA’s Earth System Research Laboratory in Boulder, Colo., was even more blunt about Texas’ chances for drought relief in the near to medium term: “It’s virtually impossible to recover from the precip]itation] deficit even if we get a rogue tropical system moving into Texas, for example.”

Seasonal US Drought Outlook, showing some improvement in parts of the large drought area.
(NOAA)
The latest drought outlook does show potential improvement in parts of Arizona and New Mexico, where the annual monsoon season is now underway (thus the Phoenix dust storm last week ), as well as portions of the Atlantic coast. But Texas, Oklahoma, as well as parts of Louisiana and Arkansas appear destined for a longer stay in a purgatory of drought and heat.

Drought conditions currently extend from Arizona eastward across the Gulf Coast into Florida, and up the Southeast coast. In Texas and many other areas, the drought began back in October, when drier than average conditions set in, and rainfall has been well below average ever since. Many longstanding records for precipitation and temperatures have fallen during this period.

Every county in Texas has been declared an agricultural disaster area, freeing up federal aid to farmers whose fields and livestock have taken a heavy toll.

According to NOAA’s Hoerling, the nine months since October 1, 2010 have been the driest nine-month period since 1895 when precipitation is averaged across Texas, Oklahoma, and New Mexico. In Texas, precipitation was more than eight inches below the average of 13.83 inches during the period, while Louisiana was 11.72 inches below its 20th century year-to-date average of about 29 inches.

“Not only have we not experienced a drought of this intensity, but neither have our parents or our grandparents,” he said.

According to the U.S. Drought Monitor 63 percent of the Southeast was in moderate-to-exceptional drought at the end of June, which was up from 51 percent at the end of May. In the South, the percent area in the worst category of drought, termed “exceptional drought” – which sounds too much like a compliment, in my opinion – increased from 28 percent to 47 percent.

The dry conditions have contributed to record heat, since without much soil moisture to evaporate; more of the sun’s energy can be devoted to heating the air. On June 26, Amarillo, Texas set an all-time high temperature record of 111 degrees F, breaking the previous record of 109 F set just two days earlier.

The state of Texas experienced its warmest June on record, while Louisiana and Oklahoma, two other states experiencing drought conditions, experienced their second-warmest June on record. The drought has also resulted in massive wildfires, with more than 4.9 million acres having gone up in smoke already this year, the most on record to date.

Palmer drought severity index from July 2, 2011
(NOAA)

It’s difficult to compare droughts, in part because there are so many different ways to measure drought conditions in the first place. Victor Murphy, climate services manager for the National Weather Service southern region, said the drought’s intensity in places such as Texas has been “pretty much unparalleled” during the past nine months. He said the drought currently ranks as Texas’ third-worst drought on record, based on the Palmer Drought Severity Index, but it is quite comparable to the top two droughts on the list, which occurred in 1956 and 1918, respectively.

There have been other droughts that lasted much longer than this one, however, and that precedent has forecasters concerned.

A renewed La Nina?

The drought was caused in part by La Nina conditions in the tropical Pacific Ocean, which altered the main storm track across North America, helping to steer storms across the northern tier, leaving southern areas desperate for rain. Although La Nina has waned, there are increasing signs that it may redevelop this fall or winter, according to the latest outlook from the Climate Prediction Center.

However, La Nina wasn’t the only force behind the drought, says Hoerling, who leads a group of climate change attribution sleuths at NOAA. For now, though, the co-conspirators remain unknown. Although climate science research shows that droughts are likely to become more intense and more frequent in a warming world, particularly in the Southwestern US, observational evidence does not yet show clear trends in drought conditions in the U.S. to date.

Hoerling says his quick analysis led him to conclude that climate change has not played a major role in this event. “This is not a climate change drought by all indications,” he said, adding that this view does not in any way refute the fact that global warming is occurring, either.

Hoerling noted that as average temperatures increase due to climate change, drought impacts would likely get worse. Drought plus heat “is just going to make a bad situation that much worse,” he said, since higher temperatures dry soils out much more rapidly. “We haven’t necessarily dealt with drought and heat at the same time in such a persistent way.”

He said the drought serves as a reminder that society needs to be more prepared for significant, relatively rare events such as this one, regardless of whether they are due to global warming or natural climate variability.

“The worst thing that we could do is not react to this drought in a way that is proactive to the consequences of the next drought,” he said.

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